\documentclass{article}
\begin{document}

% I was expecting a `,' or a `}'---line 9 of file ref1.bib
%  :
%  :   note    = {Blah},
% (Error may have been on previous line)
\cite{expecting-comma}

% Repeated entry---line 7 of file ref2.bib
%  : @article{repeated
%  :                  ,
% I'm skipping whatever remains of this entry
\cite{repeated}

% Warning--entry type for "nostyle" isn't style-file defined
% --line 13 of file ref2.bib
\cite{nostyle}

% Warning--I didn't find a database entry for "undefined"
\cite{undefined}

% Warning--to sort, need author or key in empty
% Warning--empty author in empty
% Warning--empty title in empty
% Warning--empty journal in empty
\cite{empty}

\bibliographystyle{plain}
\bibliography{ref1,ref2}
\end{document}
